1. Field of the Invention
The present invention relates to a continuous liquid infusion device for infusing transfusion liquid such as a nutrient solution and medicine such as an anti-cancer agent and an analgesic into a body at regular speed and flow rate.
2. Description of the Related Art
International Publication No. WO95/28977 discloses a typical conventional continuous liquid infusion device of this kind. This device has a structure in which liquid can be continuously infused by pressing a piston in a liquid syringe in synchronization with moving force of the piston which moves with use of a difference in pressure between a negative pressure space and atmospheric pressure, the negative pressure space being formed by a negative pressure cylinder and the piston air-tightly fitted into the negative pressure cylinder.
The conventional continuous liquid infusion device as described above requires two positions having large sliding resistance in the cylinder and the syringe in order to maintain air-tightness of the negative pressure cylinder, which causes difficulty in precise manufacturing as well as a disadvantage of poor operability in usage because large force is needed for infusing liquid.
Accordingly, the inventor of the present invention has disclosed a continuous liquid infusion device having excellent operability capable of infusing liquid with small force as Utility Model Registration No. 3068265 and Japanese Unexamined Patent Application Publication No. 2001-333980. The continuous liquid infusion device in these documents has the structure in which air-tightness between the negative pressure cylinder and the piston can be maintained at one position to reduce sliding resistance, and the liquid syringe and the negative pressure cylinder are separated so as to enable use of a liquid syringe into which liquid is infused in advance, reducing manufacturing costs and improving its operability and usability.
However, the inventor of the present invention has not been satisfied with the above techniques, further pursuing better manufacturability, reduction in the number of parts, shortening of the whole length, and the like to aggressively aim at development of a continuous liquid infusion device having further improved operability and usability with lowered manufacturing costs.